It has been shown that the neurohormone vasopressin (VP), in addition to its renal and circulatory actions, improves learning and memory consolidation, increases catecholamine metabolism in the brain and is even considered to be a neurotransmitter. Disturbance of all these mentioned parameters is associated with the aging process. However, the changes in VP physiology during aging are not well understood. We have previously shown that in old rats (30 months) VP content in the hypothalamus (HT) is about a half of that in young (2 months) or adult (12 months) rats. the impairment of VP synthesis in aged rats has not been studied. We further showed that the VP content in the neurohypophsis (NH) did not change with age, while plasma VP concentration was reduced in old rats. Whether this is due to a decreased release of VP, to an increased degradation or both in not known. To answer these questions, we propose to study the following parameters in young (2 months), adult (12 months) and old (30 month) rats: 1. The rate of synthesis of VP in the HT and VP transport to the NH using intracisternal injection of labeled phenylalanine and arginine. 2. Release of VP from the isolated NH and also from the isolated HT-NH unit following various stimuli, using the microperifusion system established in our laboratory. 3. The rate of degradation of VP in the liver perfused in situ at different concentrations of VP in the perfusate. Vasopressin will be measured by our double-antibody RIA. Our long-term goal is to elucidate the effect of aging on VP physiology and/or the role of VP in the process of aging.